1. Technical Field
The present invention relates to lens modules, particularly to a lens module that is capable of auto focusing.
2. Description of Related Art
Auto focus techniques have been widely employed in various imaging systems, including, e.g., still camera systems and video camera systems. Nowadays, there are two main auto focus methods: one is an active focus (i.e., distance metering) method, and the other one is a passive focus (i.e., focus detecting) method. In particular, the passive focus method mainly employs a charge-coupled device (CCD) and works by evaluating the amount of contrast or the phase difference in a scene. The active focus method usually utilizes an infrared light or an ultrasound emitter and a corresponding receiver in a triangular surveying system. Data generated by the triangular surveying system is converted by a microprocessor into information about a moving distance of a lenses assembly of an auto-focus imaging system, thereby enabling automatic focusing of the auto-focus imaging system.
Generally, a typical auto focus lens module includes an optical imaging assembly, an image sensor, a control unit and an actuator. The optical imaging assembly usually includes a movable lens assembly. The actuator commonly includes either a stepper motor or a voice motor, and a driving circuitry. The driving circuitry, regulated by the control unit, can drive the stepper motor or the voice motor to perform a rotational movement. In order to carry out the position adjustment of the movable lens assembly in an automatic focusing process, a mechanism (e.g., a gear assembly) has necessarily been employed to transform the rotational movement of the stepper motor or the voice motor into linear movement. However, the existence of the actuator and the gear assembly generally makes the typical auto focus lens module unduly bulky.
What is needed, therefore, is an auto focus lens module having a compact configuration.